Timing device



Jan. 6, 1953 a. E. SHAW ETAL 2,624,812

TIMING DEVICE Filed Jan. 2, 1948 3 Sheets-Sheet l I lnve nIur's BURTONE, SHAW g PHILLIP GUIFFRIDA Jan. 6, 195 3 8. E. SHAW ETAL 2,624,812

TIMING nsvxcs Filed Jan. 2, 1948 3 Sheets-Sheet 2 lnvB nInPs BURTON E.SHAW PHILLIP GUIFFRIDA Patented Jan. 6, 1,953

UNITED STATES PATENT OFFICE 2,624,812 TIMING DEVICE Burton E. Shaw, EastBoxford, and Philip Giuffrida, Lawrence, Mass, assignors to CombustionControl Corporation, Cambridge, Mass, a corporation of MassachusettsApplicationJanua-ry 2, 1948, Serial No. 262

Claims. 1

This invention relates to furnace controls and particularly to a timingor program switch suitable for controlling the starting operations offurnaces of the full-automatic, fluid fuel-burning type.

The types of fuel burners now in common use fall into three generallyrecognized classiflcae tions, manual, semi-automatic, andfull-automatic. The manual type of burner is 'both ignited and shut downby an operator. The semi-automatic type is manually ignited, but has anelectrically controlled fuel supply system which is shut down by athermostat or similar control when sufficient heat has been produced.The full-automatic type has an electrically controlled ignition systemin addition to the fuel supply system, and heating periods areinitiated-and terminated by a thermostat,pressu-re switch, cr -similarcontrol, without any-attention from an operator under normal conditions.On full-automatic burners ignition is ordinarily accomplished by passinga high-voltage spark between electrodes in the vicinity of thefuel-admitting orifice. Burners of the large capacity, industrial typemay in addition, employ a pilot burner to ignite the main burner. Toinsure safe and proper operation, the ignition, pilot, and main burnermust be put into operation in a certain sequence and at accurately timedintervals. Theoptimum delay periods between starting operations dependon the capacity and construction of the burner and the type of fuelused. For example, on a typical oil burner ignited by a gas pilot, theelectric ignition, pilot valve and burner motor are energizedsimultaneously. After an interval, generally referred to as the fuelvalve delay or ignition period, during which the pilot flame becomesestablished, the main fuel valve is opened. The pilot is leftburningthereafter for an additional period, known as post-ignition, toinsure proper ignition of the main flame. The optimum fuel valve delayperiod for different makes and capacities of burners may vary from'5 tov3.0 seconds. The post-ignition period-is ordinarily between 30 and 80seconds in duration.

To insure safe operation of the pilot ignited type of burner, it isnecessary to prevent opening of the main fuel valve if the pilot is notburning, and for this reason, a flame failure detection deviceresponsive to the pilotflame should be, in

control of themain fuel valve circuit, upon termination of the fuelvalve delay period. ,On an oil burner ignited onlybyspark electrodes,however, itis necessary, to hold themainfuel valve open for-a shorttlmeto permit ignition. For

2 this purpose, monitoring of the flame by the fl m failure control mustbe delayed for a time after opening of the fuel valve. This interval isknown as the priming period and runs concurrently with, but usually isshorter than, the post-ignition period.

From the foregoing discussion, it is apparent that a timing controldesigned for universal use in the many existing types of furnaceinstallations must be readily adjustable to suit individualrequirements. Nevertheless, to insure safe and efflcient operation, oncethe proper delay periods for a particular burner have been determined,the settings of the control device must be accurately maintained,regardless of line voltagefluctuations and other disturbing factor-snormally encountered.

It is accordingly the chief object of this invention to provide a timingcontrol of thistype which is considerably more accurate and stable inits operation than controls heretofore used for the purpose. Inparticular, this control is designed to eliminate 'errors due to linevoltage fluctuations. It is well known that large fluctuations in linevoltagearecommon in industrial installations because of the-high currentdemands of machinery and other electrically powered industrialequipment. The performance of the warp switch type of timer, for example', may be unsatisfactory insome installations because thetimedperiods are dependent on the heating effect of current through aresistance coil, and therefore on the line voltage. Errors may alsooccur in such switches due to change in characteristics of thebimetallic leaves.

Another object is to provide a control in which the delay periods may beaccurately and continuously adjusted in the field by the average factorymaintenance vman using only a common screw driver. This provisionrepresents a considerable a dvance over the controls now in common usein which the durations ofthe various periods are eithe not adjustable atall, or adjustable only in one or two steps.

Other objects are to produce a control of this type which'rnaintains itsaccuracy indefinitely, which is small and compact, but will withstandsevere usage, Which may be operated manually for observation andtesting, a'nd whichis relatively cheap to manufacture and simple toinstall. i

The invention comprises generally a small synchronous motor whichrotates a number ofcams mounted on its shaft. The cams operate springleaves which are designed'to open and close con- 3 tacts in controlcircuits of the burner. Several of the cams may be shifted to provideadjustment of the delay periods, and a suitably calibrated dial ismounted on the face of the device. The cam assembly may be rotated by ahand knob. The motor and hand knob are connected to the cam assemblythrough one-way clutches to prevent turning of the cams in the wrongdirections with possible resultant damage to the motor and cam contacts.The contacts are of high current capacity and are all readily accessiblefor cleaning. The switch here described is primarily designed foroperation with a control circuit similar to that shown in the copend-ingapplication of E. Craig Thomson, Serial No. 788,836, filed November 29,1947.

In the drawings:

Fig. 1 is a front view of the device;

Fig. 2 is a side view;

Fig; 3 is a cross-section, partly broken off, taken along lines 33 ofFig. 2; v

Fig. 4 is an exploded view of the motor shaft and cams disassembled;

Fig. 5 is a cross-section taken along lines 55 of Fig. 2;

Fig. 6 is a view similar to Fig. 1 with the dial, hand knob, rearcontacts, and some of the mounting parts omitted;

Fig. 7 is a diagram of a typical electrical circuit employing thedevice;

Fig. 8 is a graph showing the various timed periods in relation to theposition of the timer motor; and

Fig. 9 is a view, partly broken away, along lines 99 of Fig. 6.

Referring first to Figs. 1, 5, and 6, master cam I ordinarily machinedor molded from an insulating plastic, is pressed or molded onto a metalbushing II which rides on shouldered shaft I2. The shaft I2 is securedby set screw I to the shaft I3 of synchronous motor I4. The master camis hollow so as to fit over housing I6 of motor I4, for the purpose ofreducing shaft overhang to a minimum. A second plastic cam I1 is moldedonto bushing 22 which rides over bushing II. Cams l8, I9, and also madeof insulating material, and dial 2| slide over bushing 22. Bushing IIterminates in a toothed face 25 which is engaged byserrated disk 25. Thedisk is slotted in the center and fits over fiatted end 23 of shaft I2where it is yieldingly held in place by coil spring 26 secured by washer21 and cotter pins 28. The motor normally turns clockwise, as observedfrom the face of the dial, and drives the cam through engagement of theserrations of disk 25 with the teeth of face 2 3. If the motor should beincorrectly connected and revolve in the opposite direction disk 25slides over face 24 and the cam assembly is disengaged from the motor.Damage to the motor and cam contacts under such a condition is thusprevented.

Bushing 22 is grooved near its outer end to receive S-shaped leaf spring29, as shown in Fig. 6. When knob 36 is in place, set screws 3| projectinto groove 32 and engage the ends of spring 29. It is apparent thatwith this arrangement cam IT can be driven by the knob only in theclockwise direction when screws 3| engage the free ends of the spring29. This one Way clutch arrangement protects the device against damagein case the knob is turned in the Wrong direc tion.

The motor and its associated field coil I36 and core I29 are secured toback plate I26 by screws I28. A base block I23, also screwed to plateI26 4 provides support for the contact leaf s rin 4 95, 9e, 91, a1, 9|,as, and so which are sp ced f r m each other by insulating spacers I22and assembled onto the base block by means of screws I26 and I26.Further toward the rear, leaf springs til, 38, 39, and 36 (Figs. 2 and3) are similarly spaced apart by insulating spacers E32 and fastirlledto has: block I23 by screws 13!. Any suita e suppor ing frame ma i plate126 and block I23. y be used place of The synchronous motor in theexample of the device here shown is so geared down that shaft I2 makesone revolution in 120 seconds, coming to rest, when the burner is innormal operation at the point where steps 36 on cam face 35 (Figs 3 and6) has just cleared the end of leaf spring 36. this position contacts 37and ii are open In Fig. 6, it may be seen that the end of spring leaf 88is approaching step 86 of cam surface 93 and contacts are closed. On afew degrees turn of the motor spring leaf 68 drops oif steps 86 openingcontact .5. Simultaneously spring leaf 81, which is connected to leaf 88by insulatmg spacer 89 (Figs. 6 and 9 springs in, closing contacts 44.As the motor continues to rotate leaf 96 drops off the step 86 of camsurface 96 closing contacts 46. Simultaneously leaf 9 WhlCh s connectedto leaf 96 by insulating spacer 99, spr ngs in to close contacts t2(Fig. 6). At this point, the end of leaf 36 has started up rise 34 oncam surface 35. Contacts 6'! close next and, when the top of rise 34 isreached leaf 33 is forced back to close contacts 6|. As the end of leaf36 moves down the other side of ri e 34 contacts 4| open again. 7 k IWhen step II I of cam 22 reache leaf 90, which is connected to leaf 9?tgirfifiafi mg spacer 92, contacts 65 close and contacts 44 open. Theposition of cam 28 with respect to cam I 0 is adjustable within thelimits I2! and IE5 of slot I64 cf cam I9 in a manner and for a purposeto be described later. In the position shown in Fig. 6, the opening ofcontacts 44 and closing of contacts 45 occur substantiallysimultaneously with the closing of contacts 6i.

As seen in Fig. 2, leaf 9? rides over cams I8 l9 and 20. When step In ofcam 2e reachesthe end of leaf 9?, this leaf and leaf which is connectedto it through insulating spacer 98 drop infigenngt 1contacts 42.

er ur er rotation of the motor, iGI, which rides over the surface of Caif 2123 I63 (Figs. 2 and 6) drops off step II2 of cam II, openingcontacts 46. At this stage contacts and 37 are closed, and contacts ii46 open. The motor continues to rotaze t li assembly until a revolutionis completed and leaf 36 drops off step 33, opening contacts 3'1. Springleaf 39 acts as a stop for leaf 36 and insu e a sharp break of contacts3?. l S ig. 7 shows an example of a co 1 control system which isdescribed ir i r n f'e t si l 1n copending application, SerialNo. 788836 filed November 29, 1947, by E. Craig Thomson. In Fig 7 the cams areschematically indicated but con tact points corresponding to thecontacts of Figs 1, 2, 3 and 6 are correspondingly numbered combustionchamber, generally indicated as I 2 has mounted therein a main burnerI33 p1 0 (111011132. main flame 69 and a. pilot burner I34 producingpilot flame I0. Fuel to the main flam 1S supphed through blower 68 andfuel line I? controlled in a well-known manner by a solenoid valve 'I6.Fuel to the pilot is supplied through fuel line I3 controlled bysolenoid valve 74. The

5. pilot is ignited by spark electrodes 12 which are excited by ignitiontransformer 15. A name fail-' ure detection device, here illustrated asresponsive either to a photocell 62 or to a name electrode 1|, energizesrelay 60, closing contact 63 and opening contact 64, when eitherthepilot or the main flame is burning. On cooling, con tact first 41, thencontact 49, engages contact 50 and with rising temperature, theoperation is reversed. The device for initiating heating cycles is hererepresented as a conventional three wire thermostat 48 having contacts41, 49 and 56. The system also includes a power relay 65 controllingnormally open contacts'and an aux iliary relay 54, controlling normallyopen con-- tacts 55 and 51, and normally closed contact 56. The closingof contacts 50 and 49 establishes a circuit from secondary 5| through50, 41, 56 to timer motor M, and. the motor starts to revolve. Aspreviously described contact 45 o ens soon after the start of the timingcycle.- This contact is in the circuit'of the main fuel valve. Since thecircuit is at this time broken at 61, the opening of 45 has no effect,but this arrangement permits location of step 86 on cam to serve thedouble purpose of opening contact 45 and at a later point in the cycleclosing contacts 42 and 46. Contact 44 closes at the same time thatcontact 45 opens. After 42 and 46 are closed contact 37 closes, shuntingout 56 so as to establish a holding circuit for motor l4. Contact 4|then closes. Up to this time none of the operating circuits of theburner have-been energized and the burner has remained shut down. Thedelay between the starting of timer motor and the closing of contact 4|is known as the scavenging period and insures the dissipation ofunburned gases in the combustion chamber before the ignition is turnedon. I The closing of contact 4| initiates. the starting cycle bycompleting the energizing circuits of relay 54, through 58, 4|, 41-, and56 to secondary and of relay 65, through 64, 42, 44, 58, 4|, 41, and 59to secondary 5|. Relay 54 closes holding contact 55, which shuntscontact 4| and thermostat holding contact 51, which shunts 49 to 41, soas to hold relay 54 energized until 41 separates from 56, and openscontact 55. Relay65 closes its holding contact 66 and main contact 61,which completes the circuits to the burner motor 68, pilot valve '14,and ignition transformer 15. Under normal conditions the burner motorstarts to run and the pilot ignites. Soon afterward the flame failuresafeguard 6|, in response to the detection of flame by electrode H,energizes relay cc closing contact 63, which shunts contact 42 and 44.Since contact 63 is in the circuit of the main fuel valve 16, it isapparent that the pilot name must be established in order for the mainfuel valve to be opened. Contact 4| opens again after a few seconds, butrelays 54 and 65 are now held in through contact 55. After a certaindelay, which may be varied by the-setting of cams i9 and. 26-, contact45 closes. Under normal conditions, with contact 63 closed, the closingof contact 45 completes the circuit to main fuel valve 16. The mainvalve then opens and the main flame ignites shortly thereafter. Contact44 opens simultaneously with the closing of 45. As the circuit is hereshown, the energizing circuit relay 65 is then dependent on contact 63,that is, the flame failure device is in control of the system and if theflame should be extinguished, relay 60 would become deenergized openingcontact 63 and causing main relay 65 to drop out and shut down theburner. On certain types or burners, for example, those consuming oil orpulverized coal, it may be desirable to allow for a certain delay knownas the priming period between the opening of the main fuel valve andmonitoring of the flame. In this case, a jumper is connected acrossterminals 58 and 59, and contact 63 is then shunted by contact 42 for acertain period after the opening of 44. This period is adjusted by thesettin of cam 20 in a manner to be described later. At the end of thepriming period, contact 42 opens. Later in the cycle con tact 46 opens,shutting off the pilot and ignition. The interval between the closing of4| and open ing of 46, is designatedthe ignition period" and varies inlength according to the setting of em IT. The burner is then in normalrunning con= dition, with only the main flame burning. The timer motorcontinues to revolve until leaf 35 drops off step 33 breaking contact 31and leaving the cam assembly in the starting position with all the timercontacts open except contacts 45, which hold in the main fuel valvecircuit.

The relationship of the various periods in the starting cycle can bebest understood by reference to Fig. 8. Line 13 indicates the startingposition. Line 13 indicates the closing of contact 4|, which ends thescavenging period. The fuel valve delay or ignition period which beginswith the closing of 4| (line 19) may vary from zero seconds (line 19) toline 82, representing in this example approximately 30 seconds. Thepriming period starts with the end of the fuel valve delay, somewherebetween lines 19 and 82, and may vary from zero to a line approximately90 from the starting point, representing approximately thirty seconds.In the switch here shown by way of example, the zero priming period isachieved by omitting the juniper across terminals 58 and 59 aspreviously described. The opening of contact 42, which determines thepriming period may be adjusted to give between 15 and 30 seconds delay.The post ignition period starts from the end of the fuel valve delayperiod, between lines 19 and 82, and may be adjusted from zero toseconds for zero fuel valve delay, and from zero to 55 seconds for themaximum fuel valve delay of 30 seconds.

The priming period setting is intended to be made by the manufacturer ofthe control or one especially familiar with the operation of the controlsystem. The device is accordingly purposely designed so that removal ofthe dial is required.

Referring to Figs. 4 and 6, cam 20 is secured to cam l9 by screw H6which runs through slot |09 into tapped hole E8 and cam l9 and the headof which rests in groove I68 in cam 20. If the screw is loosened, cam20' may be rotated with respect to cam l9 within the limits of grooveI08. The setting shown in Fig. 6 allows leaf 91 to drop off steps Illand 3, which coincide opening contact 42 and thereby terminating thepriming period, fifteen seconds after leaf drops off step H3 closingfuel valve contacts 45. If cam 2|! is rotated counterclockwise, step ismoved so as to lag behind steps 3. Leaf 91 which extends over both camsis thus held out longer, during the revolution of the cam assembly,delayin the opening of contact 42, while leaf 96 which extends only overcam l9, continues to drop out at the same point in the cycle. Thepriming period, according to the arrangement here shown, may be extendedup to thirty seconds.

The fuel valve delay and post ignition periods are intended to be set atthe furnace installation by e, maintenance man of ordinary skill.Referring toFigs. 4 and 5, dial 2! is provided with a fuel valve scaleI31, and a post ignition scale I38. A pointer I35 rides in slot I36 nextto the fuel valve scale. This pointer and the dial are secured by screwI I which extends through slots I09, I04, and H9 in cams 20, I9, and 22and hole 8I in cam I8, and engages threaded hole I20 in cam I0. The dialis fixed to cam I9 by pin II! which extends through slot I09 in cam 20into hole I39 in the dial. When screw H0 is loosened, the dial and earnsI9 and 20 may be rotated independently of cam I0 so that step I I3 maybe positioned to give a delay in the doing of contacts 45 up to 30seconds after the closing of M by rise 34 of cam face 35 engaging leaf35. The scale I 31 iscalibrated so that the position of pointer I35indicates the length of this delay period. Since a zero fuel valve delayis ordinarily not desirable, pointer I35 is so designed as to limit theminimum setting in slot I 36 to about seconds. For special conditions,however, the pointer may be removed, so as to extend the adjustmentrange to zero.

The fuel valve adjustment is made with the cam assembly in the startingposition. With the dial and fuel valve pointer held in place, cam I! maybe rotated by the knob 30. Cam I! controls leaf NH, and the position ofstep I I2 determines the delay in closing contacts 46 which shut off theignition system of the burner. Pointer I2! is held in slot I43 by tabI49 and secured in place by screw I II which enters fiat I92 of bushing22.

Since scale I38 moves with scale I37, the position of pointers I21,indicates the period between the closing of fuel valve contacts 45 andthe opening of ignition contacts 46. Scale I38 therefore directlyindicates the post ignition period. After the settings are made, screwIII] is tightened so that the whole cam assembly moves together.

From the foregoing description, it will be clear that the switch hereindisclosed is designed to regulate the starting operations of a furnacesystem with a high degree of accuracy and reliability, The timingoperation is entirely independent of line voltage fluctuations and wearor fatigue of the switch parts, being dependent only on line frequencywhich is considerably more stable than line voltage. The effect offrequency variations is further made negligible by the gearing down ofthe timer motor. The construction of the cams and spring leaves insurespositive contact action and permits the use of heavy duty contactswherever desired. The range and simplicity of adjustments makes thedevice adaptable for use in a wide variety of burner installations.

It will be further noted that the arrangement of several of the contactsso as to operate in pairs, and the cooperating arrangement of the camsurfaces permits all the necessary timing operations to beaccomplishedwith a minimum of working parts.

Since certain changes may be made in the above-described article anddifferent embodiments of the invention could be made without departingfrom the scope thereof, it is intended that all matter contained in theabove description or shown in the accompanying drawings shall beinterpreted asillustrative only and not in a limiting sense.

What is claimed is:

1. A program switch comprising: a synchronous motor having a drive shaftfiatted toward its outer end, a master cam secured to a bushing which ismounted on said motor shaft, said bushing terminating in a toothed face;a slotted disk mounted on the flatted part of said shaft and having aserrated edge adapted to engage said toothed face; a retaining springfor holding said disk in yielding contact with said face; a second camsecured to a second bushing which is mounted freely on said first-namedbushing; a groove near, and a slot across, the end of said secondbushing; an S-shaped leaf spring lying in said groove and slot; a handlehaving inner projections for engaging the ends of said spring to drivesaid second cam; a pointer fixed to said second bushing; a dial freelymounted on said second bushing and carrying a scale over which saidpointer rides; a circumferentially slotted cam fixed to said dial; aslot in said dial coinciding with the slot in said last-named cam; asecond pointer riding in said dial slot and a second scale on said dialcooperating with said second pointer; a screw extending through saidsecond pointer and the slots in said dial and last-named cam into atapped hole in said master cam for the purpose of securing all of saidcams together; and a plurality of spring leaf contacts adapted to beoperated by said cams.

2. A program switch according to claim 1 wherein said contacts compriseseveral pairs of leaf springs, the first leaf of each pair acting as acam follower and the second leaf being substantially rigidly spaced awayfrom the first.

3. A program switch according to claim 2 having a secondcircumferentially slotted cam adjustably secured to the first-namedslotted cam, one of said cam followers riding only on said first-namedslotted cam and another of said cam followers riding on both saidslotted cams.

4. A program switch according to claim 1 having a secondcircumferentially slotted cam adjustably secured to the first-namedslotted cam. 5.A program switch according to claim 1 wherein said mastercam is recessed to receive said motor.

BURTON E. SHAW. PHILIP GIUFFRIDA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

